Spermatozoa with full capacity for motility remain immotile while residing in the rat cauda epididymidis. Initiation of rat sperm motility does not occur until ejaculation. Previous studies have demonstrated that the epididymal environment is important in maintaining this sperm quiescence. Further information has indicated that a factor, possibly a protein, present in cauda eqididymidal lumen fluid is important in maintaining the immotility of caudal epididymidal spermatozoa. The present grant application proposes to continue studies on this factor in the rat and to determine if the factor exists in other species. Using gel filtration chromatography, ion exchange chromatography, and polyacrylamide electrophoresis we will isolate the factor from the rat epididymis, determine its molecular weight, and its distribution throughout the various epididymal zones. We will determine if the factor is of epididymal or testicular origin by analyzing concentrated rete testis fluid for activity of the immotility factor and, if found, perform additional characterization of the testicular factor on the above mentioned chromatography system. We will study other laboratory species as well as human males to determine if epididymal enforcement of sperm immotility is a transspecies phenomenon. If cauda epdidymidal sperm motility does occur in the several species studied, we will determine if the quiescence is due to factors similar to those found in the rat. If species are found with motile epididymal sperm, we will determine if common factors secreted by the testis and/or epididymis of other species are absent in these species. We will determine whether human sperm are motile or immotile in situ and, therefore, whether human testicular/epididymal secretions are important in the lect uncontaminated, in vivo micropuncture samples of cauda epdidymidal content makes us uniquely capable to study this little understood but potentially important aspect of sperm-epididymal interaction.